Measurement of the production cross section of jets in association with a Z boson in 8 TeV proton-proton collisions with the ATLAS detector

This thesis presents the measurement of the production cross sections of jets in association with a Z boson in proton-proton collisions at √ s = 8 TeV with an integrated luminosity of 20.3 fb$^{−1}$ recorded by the ATLAS experiment at the Large Hadron Collider at CERN. Inclusive and differential Z/γ∗ (→ e$^{+}$e$^{−}$)+jets cross sections are measured for jets with a transverse momentum p$^{_{T}^{jet}}$ > 30 GeV and rapidity p$^{_{y}^{jet}}$ < 4.4. Z boson candidates are identified by their decay into electron pairs. In order to stringently probe the modelling of Z/γ$^{∗}$+jets production by Monte Carlo generators in regions of high-$_{T}$ phase space typical for Higgs boson decay and searches for new physics, events with high-p$_{T}$ final states are investigated. High-p$_{T}$ final states are defined as events with either p$^{_{T}^{Z}}$ > 300 GeV or $^{_{T}^{leading jet}}$ > 300 GeV. A set of four observables, sensitive to the topology of the event, are measured for the standard event selection as well as in the regions of high-p$_{T}$ phase space. The results from data are unfolded to particle level and compared to calculations of the matrix element from Monte Carlo generators Alpgen+Pythia and Sherpa interfaced to a parton shower. The results show that Sherpa tends to model Z/γ$^{∗}$+jets production in high-$_{pT}$ regions of phase space much better than Alpgen+Pythia.